Existing complex global business systems, for example, financial and airline reservation business systems, provide their commercial services to users through worldwide communication networks. These users access the commercial services via terminals or computers, also known as client nodes, connected to the communication networks. Such business systems typically use special purpose computers, also known as server nodes, to run business application programs to provide their commercial services. At the same time, these business systems also typically rely upon other special purpose computers to handle the intricacies of providing worldwide connectivity to the client nodes through the communication networks.
The users, which include business partners who interact and share information with these business systems, are usually situated all over the world. Such business partners may also run other application programs on remote business systems to provide their own type of commercial services. These users and business partners use a variety of legacy systems—terminals, or special purpose computers running application programs, which are outmoded by new technology—to communicate with the server nodes. For service reliability and efficacy, the server nodes are usually located at a central site to provide distributed network services; they carry out shared processing and storage activities to provide the required commercial services. Such server nodes are also known as back-ends. For example, users and business partners of financial and airline reservation business systems interact with the application programs on the respective back-ends to carry out transactions such as fund transfers and airline ticket bookings respectively. Messages that make up part of these transactions arrive at the central site from around the world and are usually routed via special purpose computers, known as gateway nodes or front-ends, to the distributed network of back-ends.
FIG. 1 illustrates a typical Centralized Business System 102. Most back-ends 104 are located at a central site and interconnected to form an Enterprise Local Area Network (E-LAN) 106 to provide distributed network services. Connected to a Wide Area Network (WAN) 110 are a series of client nodes 112 which are located at different geographical locations. Some server nodes which are part of the Centralized Business System 102, such as remote server node 108, are not connected to the E-LAN 106 but to this WAN 110. The client nodes 112 may use different types of terminals, printers and computers to communicate with the server nodes to access the commercial services provided by the Centralized Business System 102. To shield the back-ends 104 in the E-LAN 106 from the intricacies of providing worldwide connectivity through dissimilar communication networks, i.e., the E-LAN 106 and the WAN 110, a front-end 114 is used. An application program on the front-end 114 also translates the messages coming from the different client nodes 112 into a format in which the application programs on the back-ends 104 can understand, and vice-versa.
Common to each of the back-ends, front-end and client nodes in the above illustrated example is a communication subsystem which includes a set of communication protocols for providing connectivity to the various types of communication networks. An example of a communication subsystem is an International Standards Organization (ISO) Open Systems Interconnection (OSI) reference model. In the OSI reference model, the communication protocols are “stacked” to form a protocol stack, whereby each of the communication protocol performs a well defined function that contributes to the overall intents and purposes of the communication subsystem in providing network connectivity. FIG. 2 illustrates the relation between two communication protocols, also known as protocol “layers” 206, 208 in the context of a protocol stack, at their interface 202 where messages 204 are transferred. A protocol layer N 206 implements its services, for example, fast and expensive communication or slow and cheap communication, used by another protocol layer N+1 208. Hence, in this example, the protocol layer N 206 is known as a service provider and the protocol layer N+1 208 is known as a service user. The protocol layer N 206 provides its services to the protocol layer N+1 208 at service access points 210 (SAPs), where each SAP identifies a resource within the protocol layer. Each of the messages 204 “passes” through these SAPs 210 as they are conveyed between the back-ends and the front-end, or the front-end and the client nodes, to form meaningful business transactions.
While the above examples of complex global business systems using special purpose computers to provide commercial services and worldwide connectivity have achieved wide commercial implementation, they suffer from disadvantages. Many of the back-ends and front-ends of these existing business systems use outmoded technology. As a result, the application programs on these back-ends and front-ends are costly and difficult to enhance or modify. In addition, such business systems do not allow new client connections to be easily added via new communication protocols, or to leverage off evolving technologies like the Internet. To overcome these limitations, efforts are underway to migrate existing business systems to “open” business systems. The aim of such efforts is to functionally replace the existing business systems with open business systems, i.e., business systems that are open for communication with any other systems, while additionally providing a wide range of connectivity, extensibility and fault tolerance.
While a large number of client nodes exists and are connected to existing business systems, each of these client nodes employs its own communication subsystem. As a result, each of these communication subsystems may use different protocol layers, and therefore a different protocol stack, to communicate with the back-ends. The need to provide connectivity to a wide range of existing client nodes, and new client nodes, requires that the communication subsystems of the front-ends are able to flexibly mix and match a myriad of protocol layers. In turn, the need to be able to flexibly mix and match a myriad of protocol layers requires a well-defined interface between adjacent protocol layers in a protocol stack.
As existing business systems are migrated to open business systems, the open business systems should not only provide the flexibility to adapt to the quick market changes, but also interoperate with the variety of connected legacy systems. The legacy systems usually have their own proprietary communication subsystems. Since a large number of legacy systems is in use, and each of them stacks the protocol layers in its own way, it is necessary to provide means to develop and implement proprietary protocol layers so that the migration is easier and cost effective.
In the event of node failures, the communication subsystems must be able to recover quickly and restore the protocol stacks so that communication may resume. Therefore, the need to facilitate such recovery activities is highly desired in a quick-recovery communication subsystem.
As newer application programs are developed and older application programs are migrated, it is also necessary that these application programs be shielded from the intricacies of the communication subsystems. Hence, it is important to draw a distinction between application programs and communication subsystems by having well-defined interfaces between the two.
Accordingly, the present invention provides a well-defined interface between adjacent protocol layers in a protocol stack, a means to develop and implement new or proprietary protocol layers, a quick-recovery communication subsystem and a well-defined interface between an application program and a communication subsystem.